Methods for measuring greenhousegas emissions from sanitation andwastewater management systems

The sanitation sector plays a crucial role in greenhouse gas emissions, contributing over half a billion tonnes of CO2 equivalents annually. This is approximately equivalent to 1.3% of global greenhouse gas emissions. However, the true scale of these emissions might be even larger, considering that emissions from sanitation systems have historically been underestimated in national and subnational emissions inventories due to limited empirical data on the quantity of emissions from various sanitation technologies across the entire sanitation chain (Lambiasi et al., 2024). This is especially the case in low- and middle-income countries, where rapidly growing urban areas have heterogeneous sanitation infrastructure configurations, with both sewer-based and non-sewered sanitation systems.

Sanitation systems that do not rely on sewers, including technologies such as pit latrines, composting toilets and septic tanks, are often not adequately covered in emissions inventories (Manga & Muoghalu, 2024).
Greenhouse gas emissions inventories are typically based on methods from the IPCC Guidelines for National Greenhouse Gas Inventories (Rypdal et al., 2006), spread across three tiers:

Tier 1, is the most basic level, utilizing global emission factors and default values, suitable for circumstances where country-specific data are limited.
Tier 2, includes more detailed methodologies, employing country-specific emission factors and activity data, thus offering improved accuracy over Tier 1.
Tier 3, the most sophisticated level, involves comprehensive and detailed methodologies, including higher resolution activity data and countryspecific emission factors, often incorporating direct measurement and
modelling approaches.

Each ascending tier represents a progression in data specificity and methodological complexity, reflecting a trade-off between accuracy and resource requirements. Estimates of greenhouse gas emissions from sanitation systems are often made using Tier 1 and Tier 2 methods, but the emission factors therein have
limitations and the assumptions behind them might not be universally applicable (Diaz-Valbuena et al., 2011; Johnson et al., 2022), which contributes to significant uncertainties in results.

source:

https://www.sei.org/publications/methods-greenhouse-gas-emissions-sanitation